Process for the ammonia and methanol co-production

ABSTRACT

A process for ammonia and methanol co-production in a plant comprising a first primary reforming section (11) and a secondary reforming section (12) arranged in series, an ammonia synthesis section (13) and a methanol synthesis section (22), is distinguished by the fact that ammonia and methanol are produced in independent synthesis processes where the heat required for the reforming reaction in the methanol process is advantageously obtained by utilizing the high heat content present in the gas flow coming from the secondary reforming section (12) of the ammonia process.

FIELD OF APPLICATION

The present invention relates to a process for the ammonia and methanolco-production in a plant comprising a first primary reforming sectionand a secondary reforming section arranged in series, an ammoniasynthesis section and a methanol synthesis section, said processcomprising the steps of:

feeding methane and steam to the first primary reforming section;

reacting the methane and steam in the first primary reforming sectionand successively in the secondary reforming section to obtain a firstgaseous phase comprising CO, CO₂ and H₂.

In the description given below and in the following claims, the term:"in-situ" modernization, is understood to mean the on-site modificationof a pre-existing reactor in order to improve its performance and obtaine.g. greater production capacity and/or greater conversion yield and/orreduction in energy consumption.

In the description given below and in the following claims, the term:`synthesis section`, is understood to mean generally all of that part ofthe plant concerned with ammonia or methanol production andoperationally located downstream of the reforming sections.

In the description given below and the following claims, the term:`methane`, is understood to mean generally a raw material source ofhydrogen and carbon, such as e.g. methane itself or a mixture of liquidand/or gaseous hydrocarbons such as natural gas and naphtha.

The present invention also relates to a plant for ammonia and methanolco-production for carrying out the above mentioned process, as well asto a modernization method for an ammonia synthesis plant and to amodernization method for an ammonia and methanol co-production plant.

As known, there is an ever growing requirement in the field of ammoniaand methanol co-production to provide synthesis processes easy toimplement, which allow achievement of ever higher production capacitiesat low operating and investment costs and at low energy consumption.

PRIOR ART

For the purpose of meeting the above mentioned requirement, there haverecently been proposed in the field synthesis processes for ammonia andmethanol co-production, wherein a flow of gas rich in CO, CO₂ and H₂coming from the secondary reforming section of an ammonia synthesisplant, is diverted to a synthesis section for methanol production. Theunreacted gas is subsequently reintroduced into the synthesis section ofthe ammonia plant.

Although advantageous in some ways, the above described processesexhibit a series of drawbacks, the first of which is that the productioncapacity of ammonia and that of methanol are strictly correlated anddepend mainly on the methane and steam load which can be fed to thereforming sections.

In other words, as the total production capacity of the co-productionplant operating in accordance with these processes is substantiallydetermined by the loading capacity of the reforming sections, in afull-capacity operating situation an increase in the production ofmethanol causes inevitably an approximately equivalent reduction in theammonia production, and vice versa.

This means that if it is desired to obtain high production capacity ofboth ammonia and methanol it is necessary, according to the prior artprocesses, to size the reforming sections correspondingly so that theyare capable of supporting a load of reagents permitting achievement ofthe desired production capacity. In addition, the ammonia and methanolsynthesis sections must also be oversized to meet any load increasescaused by changes in methanol and ammonia production.

Consequently, if high production capacity of both ammonia and methanolis required, the co-production plant which must be provided forimplementation of the above mentioned processes exhibits considerablestructural complexity, high investment and operating costs, and highenergy consumption.

Because of these disadvantages, the prior art ammonia and methanolco-production processes have heretofore found slight application despitethe growing demand in the industry.

SUMMARY OF THE INVENTION

The problem underlying the present invention is to provide a process forammonia and methanol co-production which would be simple to carry outand permit achieving of high production capacity of both ammonia andmethanol with low investment and operation costs and low energyconsumption.

This problem is solved according to the present invention by a processfor ammonia and methanol co-production of the above mentioned type,which is characterized in that it comprises the steps of:

feeding methane and steam to a reaction zone defined in a second primaryreforming section of the `exchanger` type;

feeding the first gaseous phase externally to the reaction zone in thesecond primary reforming section;

reacting the methane and steam in the reaction zone by indirect heatexchange with the first gaseous phase to obtain a second gaseous phasecomprising CO, CO₂ and H₂ ;

feeding the first gaseous phase coming from the second primary reformingsection to the ammonia synthesis section;

feeding the second gaseous phase coming from the second primaryreforming section to the methanol synthesis section.

In the description given below and in the following claims, the term:`primary reforming section of the `exchanger` type` is understood tomean a primary reforming section for the production of CO, CO₂ and H₂,in which the reaction heat instead of being supplied by combustion of afuel (e.g. natural gas or naphtha), it is supplied by indirect heatexchange with a hot gas flow fed to this section. In this specific casethe hot gas flow is represented by the first gaseous phase coming fromthe secondary reforming section.

Reformers of the `exchanger` type are generally known in the state ofthe art and are usually employed in ammonia synthesis processes inreplacement of the primary reformer.

These reformers define within them a reaction zone through which thegaseous reagents pass. The reforming reaction is made possible by theheat transmitted by a hot gas flowing externally to the reaction zone.

Reformers of this type consist for example of a plurality of pipesfilled with catalyst, outside of which (shell side) is made to flow ahot gas which yields reaction heat by indirect heat exchange to a coldergas which flows in the pipes (tube side) reacting.

The reformer of the `exchanger` type can also be provided by means of aplurality of contiguous chambers alternately filled with catalyst,wherein hot gas and cold gas are made to flow in the empty chambers andin the filled chambers, respectively. In this case, the chambers aremade e.g. in mutually parallel walls or concentric cylinders.

Advantageously, thanks to the process according to the present inventionit is possible to achieve an independent production of ammonia andmethanol, which allows to obtain high production capacities in a simpleway, with low investment and operating costs and with low energyconsumption.

Indeed, according to the present invention, the high heat content in thefirst gaseous phase coming from the secondary reforming section, isadvantageously utilized as reaction heat to produce in a second primaryreforming section a second gaseous phase comprising CO, CO₂ and H₂ forthe methanol synthesis process.

In this manner, the synthesis gas production for ammonia and methanol nolonger takes place in common reforming sections, with all thedisadvantages thereof with reference to the prior art co-productionprocesses. The process according to the present invention calls forproduction of methanol synthesis gas in a second, independent, primaryreforming section.

Advantageously, this second primary reforming section is fed withmethane and steam which react by indirect heat exchange with a gaseousphase coming from the secondary reforming section of the ammoniaprocess, with recovery of the heat contained in the gaseous phase whileavoiding the use of energy sources external to the co-production processsuch as the fuels generally employed in reforming sections.

Preferably, the temperature of the first gaseous phase coming from thesecondary reforming section and fed to the second primary reformingsection is between 900° C. and 1100° C., so as to supply heat ensuringnearly complete conversion of the methane and steam fed to the secondprimary reforming section.

Preferably the process according to the present invention comprises theadditional steps of:

taking at least part of said second gaseous phase coming from saidsecond primary reforming section;

feeding this at least part of the second gaseous phase to the firstprimary reforming section.

Thanks to this particular embodiment of the present invention, it ispossible to control the quantity of gas to be sent to the methanolsynthesis section according to the quantity of methanol it is desired toproduce. In addition, in this manner it is also possible to meet asituation in which methanol production is temporarily not required forreasons of market demand or for maintenance of the synthesis section.

The excess gas produced in the second primary reforming section andcomprising CO, CO₂ and H₂ not sent to the methanol synthesis section isadvantageously recycled to the first primary reforming section to reducethe methane and steam load to be fed to the first primary reformingsection and consequently also heat consumption of this section.

Advantageously the co-production process according to the presentinvention also comprises the additional steps of:

taking a purge gaseous flow comprising CO, CO₂ and H₂ coming from themethanol synthesis section;

feeding this purge gaseous flow to the first primary reforming section.

In this manner, the purge gas coming from the methanol synthesis sectionand rich in CO, CO₂ and H₂ can be advantageously recovered and recycledto the first primary reforming section to achieve also in this case areduction of the methane and steam load to be fed to the first primaryreforming section and consequently of the heat consumption of thissection and of the total energy consumption of the co-production plant.

To implement the above mentioned process the present inventionadvantageously makes available a plant for ammonia and methanolco-production comprising:

a first primary reforming section and a secondary reforming sectionarranged in series to obtain a first gaseous phase comprising CO, CO₂and H₂ ;

means of feeding methane and steam to the first primary reformingsection;

an ammonia synthesis section;

a methanol synthesis section;

characterized in that it comprises:

a second primary reforming section of the `exchanger` type to obtain asecond gaseous phase comprising CO, CO₂ and H₂ ;

means of feeding methane and steam to a reaction zone defined in thesecond primary reforming section;

connection means between the secondary reforming section and the secondprimary reforming section for feeding the first gaseous phase externallyto the reaction zone;

means for indirect heat exchange between the first gaseous phase and themethane and steam in the second primary reforming section;

connection means between the second primary reforming section and themethanol synthesis section for feeding to the latter a second gaseousphase comprising CO, CO₂ and H₂ ;

connection means between the second primary reforming section and theammonia synthesis section for feeding to the latter said first gaseousphase.

In accordance with another aspect of the present invention there is alsomade available a method of modernizing an ammonia synthesis plant of thetype comprising a first primary reforming section and a secondaryreforming section arranged in series to obtain a first gaseous phasecomprising CO, CO₂ and H₂, means for feeding methane and steam to thefirst primary reforming section, an ammonia synthesis section, saidmethod comprising the steps of:

providing a methanol synthesis section;

providing a second primary reforming section of the `exchanger` type;

providing means for feeding methane and steam to a reaction zone definedin the second primary reforming section;

providing connection means between the secondary reforming section andthe second primary reforming section for feeding the first gaseous phaseexternally to the reaction zone;

providing means for indirect heat exchange between the first gaseousphase and the methane and steam in the second primary reforming section;

providing connection means between the second primary reforming sectionand the methanol synthesis section for feeding to the latter a secondgaseous phase comprising CO, CO₂ and H₂ ;

providing connection means between the second primary reforming sectionand the ammonia synthesis section for feeding to the latter said firstgaseous phase.

In accordance with another aspect of the present invention, there isalso made available a method of modernizing an ammonia and methanolco-production plant of the type comprising a first primary reformingsection and a secondary reforming section arranged in series to obtain afirst gaseous phase comprising CO, CO₂ and H₂, means for feeding methaneand steam to the first primary reforming section, an ammonia synthesissection, a methanol synthesis section, said method comprising the stepsof:

providing a second primary reforming section of the `exchanger` type;

providing means for feeding methane and steam to a reaction zone definedin the second primary reforming section;

providing connection means between the secondary reforming section andthe second primary reforming section for feeding the first gaseous phaseexternally to the reaction zone;

providing means of indirect heat exchange between the first gaseousphase and the methane and steam in the second primary reforming section;

providing connection means between the second primary reforming sectionand the methanol synthesis section for feeding to the latter a secondgaseous phase comprising Co, CO₂ and H₂ ;

providing connection means between the second primary reforming sectionand the ammonia synthesis section for feeding to the latter said firstgaseous phase.

Thanks to the above mentioned modernization methods for an existingplant it is possible to obtain an ammonia and methanol co-productionprocess simple to carry out, capable of achieving high productioncapacities of both ammonia and methanol at low operating and investmentcosts and with low energy consumption.

The characteristics and advantages of the present invention are setforth in the description of an embodiment thereof given below by way ofnon-limiting example with reference to the annexed FIGURE.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 shows a block diagram of the ammonia and methanol co-productionprocess according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a block diagram illustrating the steps of the ammonia andmethanol co-production process in accordance with the present invention.

This process permits simultaneous achievement of high productioncapacity of ammonia (e.g. between 1000 and 2500 metric tons per day) andmethanol (e.g. between 700 and 1700 metric tons per day).

Reference number 10 indicates generally a portion of the block diagramillustrating the steps of the ammonia production process.

In this portion 10, blocks 11, 12 and 13 indicate respectively a firstprimary reforming section, a secondary reforming section and an ammoniasynthesis section. The latter includes in addition to the actualsynthesis section, the high- and low-temperature CO conversion sections,the CO₂ separation section and the methanation section. The abovementioned primary and secondary reforming sections are catalytic.

Reference number 20 indicates generally a portion of the block diagramillustrating the steps of the methanol production process.

In this portion 20, blocks 21 and 22 indicate respectively a secondprimary reforming section and a methanol synthesis section. The latteralso includes in addition to the actual synthesis section, the H₂ Ocondensation and separation section and the methanol purificationsection.

Advantageously, the second primary reforming section indicated by theblock 21 is of the `exchanger` type, and preferably of the type equippedwith a plurality of pipes filled with catalyst in which the reformingreaction takes place.

To the first primary reforming section indicated by the block 11 is fedflow line 1, which represents a first gaseous flow comprising methaneand steam. The temperature of this first gaseous flow is theconventional temperature for an ammonia plant, e.g. 300-650° C.

Passing through the first primary reforming section and the secondaryreforming section (blocks 11 and 12), the methane and steam contained inthe first gaseous flow react to obtain a first gaseous phase comprisingCO, CO₂ and H₂.

The flow line 2 represents this first gaseous phase coming from thesecondary reforming section indicated by the block 12. The temperatureof the gas flow 2 is preferably between 980° C. and 1050° C.

Advantageously, the flow line 2 traverses on the shell side the secondprimary reforming section represented by the block 21 where it coolsdown by indirect heat exchange with a gaseous flow comprising methaneand steam fed tube side to the block 21, and indicated by the flow line3.

Upon outlet from the second primary reforming section (block 21), thegas flow 2 is fed to the ammonia synthesis section (block 13) at atemperature between 30° C. and 600° C.

Upon outlet from block 13 the flow 2 contains mainly ammonia.

The gas flow represented by the flow line 3 is fed to the second primaryreforming section (block 21) at a temperature between 200° C. and 600°C. Here the gas flow 3 reacts advantageously by indirect heat exchangewith the gas flow indicated by the flow line 2, to obtain a secondgaseous phase comprising CO, CO₂ and H₂.

The flow line 4 indicates this second gaseous phase coming from thesecond primary reforming section (block 21). The temperature of the gasflow 4 is generally between 700° C. and 1000° C.

The gas flow 4 is fed into the methanol synthesis section represented byblock 22. Upon outlet from the block 22 the flow 4 contains mainlymethanol.

The operating conditions of the synthesis sections for the production ofammonia or methanol (blocks 13 and 22 respectively), as well as thetypes of reaction taking place in them, are the conventional ones of anammonia and methanol plant respectively, known to those skilled in theart and therefore not described in greater detail.

The pressure of the gas flows 1 to 4 is preferably between 1 bar and 60bar.

In accordance with the co-production process according to the presentinvention a first flow of methane and steam is fed to a first primaryreforming section (block 11) and is reacted in this reforming sectionand subsequently in a secondary reforming section (blocks 11 and 12) toobtain a first gaseous phase comprising CO, CO₂ and H₂.

Advantageously, in accordance with further steps of the presentinvention, a flow of methane and steam is fed to a reaction zone definedin a second primary reforming section (block 21). At the same time, thefirst gaseous phase is fed externally to the reaction zone of the secondprimary reforming section. Within this reaction zone, methane and steamare reacted by indirect heat exchange with the first gaseous phase toobtain a second gaseous phase comprising CO, CO₂ and H₂. The firstgaseous phase coming from the second primary reforming section is thenfed to an ammonia synthesis section (block 13), while the second gaseousphase is fed to a methanol synthesis section (block 22).

In this manner, ammonia and methanol are produced in independentsynthesis processes, where the heat required for the methane reformingreaction in the methanol process is advantageously obtained by utilizingthe high heat content in the gas flow coming from the secondaryreforming section of the ammonia process.

In accordance with another particularly advantageous embodiment of thepresent invention, but not shown, the co-production process comprisesthe additional step of cooling the second gaseous phase (flow line 4)coming from the second primary reforming section (block 21) by indirectheat exchange with cooling water, to obtain high pressure andtemperature steam e.g. between 5 bar and 130 bar and between 150° C. and550° C. respectively.

So doing, the heat of the gaseous phase coming from the second primaryreforming section is advantageously recovered for production of steamwith a high heat level, which can be used depending on requirements e.g.in the other sections of the ammonia and methanol co-production plant.

The temperature of the gas flow 4 which underwent the above mentionedcooling step is preferably between 30° C. and 300° C.

The heat in the gas flow 4 coming from the block 21 can alternatively berecovered to preheat by indirect heat exchange the methane or thegaseous flow comprising methane and steam to be fed to the secondprimary reforming section.

In accordance with an alternative embodiment of the process according tothe present invention, part of the second gaseous phase (flow line 4)coming from block 21 can be advantageously diverted to the first primaryreforming section (block 11) of the ammonia process. This permitsadapting the methanol process production capacity depending on thedesired quantity of methanol and at the same time to reduce the methaneload to be fed to the ammonia process with resulting saving of rawmaterials and energy.

In FIG. 1, this embodiment is shown in broken lines by flow line 5.

In case only ammonia production is requested, then all the secondgaseous phase coming from block 21 is advantageously sent (flow line 5)to the first primary reforming section (block 11) of the ammoniaprocess, as shown in FIG. 1, or directly to the secondary reformingsection (block 12).

In another alternative and particularly advantageous embodiment of theprocess according to the present invention, a purge gaseous flowcomprising CO, CO₂ and H₂ coming from the methanol synthesis section(block 22) is sent to the first primary reforming section (block 11) ofthe ammonia process to obtain a further lightening of the methane loadto be fed to this reforming section.

The pressure and the temperature of the purge gaseous flow fed to thefirst primary reforming section are generally between 1 bar and 60 barand between 30° C. and 600° C. respectively.

In FIG. 1, this embodiment is shown in broken lines by flow line 6.

The ammonia and methanol co-production plant according to the presentinvention includes the sections represented by the blocks 11-13 and21-22 of FIG. 1.

At the inlet and between the sections making up the above mentionedplant are provided suitable feeding and connection means respectively oftypes known in the industry, e.g. ducts, piping and the like representedschematically by the flow lines 1-6 of FIG. 1.

Inside the second primary reforming section represented by the block 21are also provided suitable means for indirect heat exchange between thegas flows 2 and 3. These means can comprise one or more heat exchangers.

Advantageously, the plant according to the present invention alsoprovides a cooling section (not shown) for cooling the gas flow 4 comingfrom block 21 by indirect heat exchange with cooling water. A coolingsection of this type can comprise e.g. a boiler for steam production.

In order to increase the methanol production, a gas flow comprising CO₂(not shown) is advantageously added to flow line 3 or 4, preferably toflow line 4.

In fact, since the gas flowing through line 4 is generally very rich inH₂, the above addition allows an improvement in the stoichiometric ratioCO₂ /H₂ which results in an improvement of the methanol synthesisconditions.

In accordance with the present invention, the method of modernizing anexisting ammonia and methanol co-production plant comprising a firstprimary reforming section and a secondary reforming section (blocks 11and 12) arranged in mutual series, an ammonia synthesis section (block13) and a methanol synthesis section (block 22), advantageously providesthe steps of providing a second primary reforming section (block 21) ofthe `exchanger` type comprising means suitable for indirect heatexchange, and of providing appropriate means for feeding to the secondprimary reforming section (block 21) and connection between thesecondary reforming section and the second primary reforming section(blocks 12 and 21) as between the second primary reforming section andthe ammonia and methanol synthesis sections (blocks 21, 13, 22).

The method for modernization of an existing ammonia synthesis plantaccording to the present invention provides the additional step ofproviding, in addition to the second primary reforming section, also amethanol synthesis section (block 22).

Advantageously, in an alternative embodiment of the above modernizationmethods, not shown, a cooling section for cooling the gas flow 4 byindirect heat exchange with cooling water for the production of steam athigh heat level, is provided between blocks 21 and 22.

In addition, according to another embodiment of the modernizationmethods in accordance with the present invention, suitable connectionmeans between the second and first primary reforming sections (blocks 21and 11) and between the methanol synthesis section and the first primaryreforming section (block 11) are advantageously provided. In this mannerit is possible to recover excess CO, CO₂ and H₂ from the methanolsynthesis process and send it to the ammonia synthesis process tolighten the methane load to be sent to the reforming sections of theammonia plant and thus achieve a reduction in energy and raw materialconsumption.

In the special situation in which only ammonia is intended to beproduced, then the above modernization methods advantageously allow anincrease in the production of the reforming sections with respect to anpre-existing ammonia synthesis plant, thanks to the provision of thesecond primary reforming section.

From the foregoing, the numerous advantages achieved by the presentinvention are clear. In particular there is provided an ammonia andmethanol co-production process simple to implement, capable of achievinghigh production capacities both for ammonia and methanol with lowoperating and investment costs and low energy consumption. Moreover, inthe case of modernization of an ammonia synthesis plant or an ammoniaand methanol co-production plant it is possible to achieve highproduction capacity of methanol while holding unchanged the ammoniaproduction capacity.

What is claimed is:
 1. Process for the ammonia and methanolco-production in a plant comprising a first primary reforming sectionand a secondary reforming section arranged in series, an ammoniasynthesis section and a methanol synthesis section, said processcomprising the steps of:feeding methane and steam to said first primaryreforming section; reacting said methane and steam in said first primaryreforming section and subsequently in said secondary reforming sectionto obtain a first gaseous phase comprising CO, CO₂ and H₂ ;the processcomprising the steps of: feeding methane and steam to a reaction zonedefined in a second primary reforming section of the `exchanger` type;feeding said first gaseous phase externally to said reaction zone insaid second primary reforming section; reacting in said reaction zonesaid methane and steam by indirect heat exchange with said first gaseousphase to obtain a second gaseous phase comprising CO, CO₂ and H₂ ;feeding said first gaseous phase coming from said second primaryreforming section to said ammonia synthesis section; and feeding saidsecond gaseous phase coming from said second primary reforming sectionto said methanol synthesis section.
 2. Process according to claim 1,wherein the temperature of the first gaseous phase fed to the secondprimary reforming section is between 900° C. and 1100° C.
 3. Processaccording to claim 1, further comprising the additional step of coolingsaid second gaseous phase coming from said second primary reformingsection by indirect heat exchange with cooling water to obtain highpressure and temperature steam.
 4. Process according to claim 1, furthercomprising the additional steps of:taking at least part of said secondgaseous phase coming from said second primary reforming section; andfeeding said at least part of said second gaseous phase to said firstprimary reforming section.
 5. Process according to claim 1, furthercomprising the additional steps of:taking a purge gaseous flowcomprising CO, CO₂ and H₂ coming from said methanol synthesis section;and feeding said purge gaseous flow to said first primary reformingsection.
 6. Plant for ammonia and methanol co-production comprising:afirst primary reforming section (11) and secondary reforming section(12) arranged in series to obtain a first gaseous phase comprising CO,CO₂ and H₂ ; means (1) for feeding methane and steam to said firstprimary reforming section (11); a methanol synthesis section (13) and anammonia synthesis section (22) disposed in parallel in the plant forcontemporaneous production of ammonia and methanol;further comprising: asecond primary reforming section (21) of the `exchanger` type to obtaina second gaseous phase comprising CO, CO₂ and H₂ ; means (3) for feedingmethane and steam to a reaction zone defined in said second primaryreforming section (21); connection means (2) between said secondaryreforming section (12) and said second primary reforming section (21)for feeding externally to said reaction zone said first gaseous phase;means for indirect heat exchange between said first gaseous phase andsaid methane and steam in said second primary reforming section (21);direct connection means (4) connecting said second primary reformingsection (21) to said methanol synthesis section (22) for feeding to themethanol synthesis section a second gaseous phase comprising CO, CO₂ andH₂ for the production and methanol; and direct connection means (2)connecting said second primary reforming section (21) to said ammoniasynthesis section (13) for feeding to the ammonia synthesis section saidfirst gaseous phase for the production of ammonia.
 7. Plant according toclaim 6, further comprising a section in fluid communication with saidmethanol synthesis section (22), for cooling said second gaseous phasecoming from said second primary reforming section (21) by indirect heatexchange with cooling water.
 8. Plant according to claim 6, furthercomprising connection means (5) between said second primary reformingsection (21) and said first primary reforming section (11) for feedingto the first primary reforming section at least part of said secondgaseous phase coming from said second primary reforming section (21). 9.Plant according to claim 6, further comprising connection means (6)between said methanol synthesis section (22) and said first primaryreforming section (11) for feeding to the first primary reformingsection a purge gaseous flow comprising CO, CO₂ and H2 coming from saidmethanol synthesis section (22).
 10. Method of modernizing an ammoniasynthesis plant comprising a first primary reforming section (11) and asecondary reforming section (12) arranged in series to obtain a firstgaseous phase comprising CO, CO₂ and H₂, means (1) for feeding methaneand steam to said first primary reforming section (11), an ammoniasynthesis section (13), said method comprising the steps of:providing amethanol synthesis section (22) in parallel with said ammonia synthesissection; providing a second primary reforming section of the `exchanger`type (21); providing means (3) for feeding methane and steam to areaction zone defined in said second primary reforming section (21);providing connection means (2) between said secondary reforming section(12) and said second primary reforming section (21) for feedingexternally to said reaction zone said first gaseous phase; providingmeans for indirect heat exchange between said first gaseous phase andsaid methane and steam in said second primary reforming section (21);providing direct connection means (4) between said second primaryreforming section (21) and said methanol synthesis section (22) fordirectly feeding to the methanol synthesis section a second gaseousphase comprising CO, CO₂ and H₂ for methanol production; providingdirect connection means (2) between said second primary reformingsection (21) and said ammonia synthesis section (13) for directlyfeeding to the ammonia synthesis section said first gaseous phase forthe production of ammonia contemporaneously with the production ofmethanol.
 11. Method according to claim 10, further comprising providinga section for cooling said second gaseous phase coming from said secondprimary reforming section by indirect heat exchange with cooling waterin fluid communication with said methanol synthesis section (22). 12.Method according to claim 10, further comprising providing connectionmeans (5) between said second primary reforming section (21) and saidfirst primary reforming section (11) for feeding to the first primaryreforming section at least part of said second gaseous phase.
 13. Methodaccording to claim 10, further comprising providing connection means (6)between said methanol synthesis section (22) and said first primaryreforming section (11) for feeding to the first primary reformingsection a purge gaseous flow comprising CO, CO₂ and H₂ coming from saidmethanol synthesis section.
 14. Method of modernizing an ammoniasynthesis plant comprising a first primary reforming section (11) and asecondary reforming section (12) arranged in series to obtain a firstgaseous phase comprising CO, CO₂ and H₂, means (1) for feeding methaneand steam to said first primary reforming section (11), an ammoniasynthesis section (13), a methanol synthesis section (22) disposed inparallel with said ammonia synthesis section for coproduction of ammoniaand methanol, said method comprising the steps of:providing a secondprimary reforming section of the `exchanger` type (21); providing means(3) for feeding methane and steam to a reaction zone defined in saidsecond primary reforming section (21); providing connection means (2)between said secondary reforming section (12) and said second primaryreforming section (21) for feeding externally to said reaction zone saidfirst gaseous phase; providing means for indirect heat exchange betweensaid first gaseous phase and said methane and steam in said secondprimary reforming section (21); providing direct connection means (4)for directly connecting said second primary reforming section (21) tosaid methanol synthesis section (22) for directly feeding to themethanol synthesis section a second gaseous phase comprising CO, CO₂ andH₂ for production of methanol; and providing direct connection means (2)between said second primary reforming section (21) and said ammoniasynthesis section (13) for directly feeding to the ammonia synthesissection said first gaseous phase for the production of ammoniacontemporaneously with the production of methanol.
 15. Method accordingto claim 11, further comprising providing a section for cooling saidsecond gaseous phase coming from said second primary reforming sectionby indirect heat exchange with cooling water in fluid communication withsaid methanol synthesis section (22).
 16. Method according to claim 11,further comprising providing connection means (5) between said secondprimary reforming section (21) and said first primary reforming section(11) for feeding to the first primary reforming section at least part ofsaid second gaseous phase.
 17. Method according to claim 11, furthercomprising providing connection means (6) between said methanolsynthesis section (22) and said first primary reforming section (11) forfeeding to the first primary reforming section a purge gaseous flowcomprising CO, CO₂ and H₂ coming from said methanol synthesis section.